1. Field of the Invention
The present invention relates to a lens barrel, used in an optical system for an optical device such as a camera, for changing its power and adjusting its focus.
2. Related Background Art
Conventionally known as a lens barrel, used in an optical system for an optical device such as a camera, for changing its power and adjusting its focus is one comprising front and rear group lenses in which the rear group lens is attached to a movable cylinder expandable from a camera body whereas the front group lens is attached to a front cylinder further expandable from the movable cylinder as disclosed in Japanese Patent Application Laid-Open No. HEI 11-218659. The lens barrel disclosed in this publication aims at adjusting the focus by appropriately moving the rear group lens by using a cam groove formed at the inner periphery of the movable cylinder.
Also known as a lens barrel, used in an optical system for an optical device such as a camera, for changing its power and adjusting its focus is one having four lens groups, all of which are attached to a frame expandable from a camera body and are appropriately moved in the optical axis direction by utilizing a cam mechanism, so as to change the power and adjust the focus as disclosed in Japanese Patent Application Laid-Open No. HEI 7-20369.
The lens barrel disclosed in the latter publication comprises a barrier blade, disposed in front of a taking optical system, for opening and closing an optical path; a lens driving mechanism for advancing and retracting a part of the taking optical system in the optical axis direction upon a focusing operation of the taking optical system; a barrier driving mechanism for driving the barrier blade to open and close; a first transmission mechanism for transmitting a driving force of a driving source to the lens driving mechanism; and a second transmission mechanism for transmitting the driving force of the driving source to the barrier driving mechanism, in which the transmission of the driving force to the second transmission mechanism is appropriately switched via a clutch mechanism. It switches the clutch mechanism by utilizing a pivotal member, so as to enhance the space efficiency and reduce the size of camera.
However, the above-mentioned lens barrels may have problems as follows. Namely, if an external force is exerted on the lens barrel disclosed in Japanese Patent Application Laid-Open No. HEI 11-218659 so that a distortion occurs between the movable and front cylinders constituting the lens barrel, then the optical axis or posture may deform between the front and rear group lenses.
If an external force is exerted on the lens barrel disclosed in Japanese Patent Application Laid-Open No. HEI 7-20369 so that a distortion occurs between the first lens group frame and rotary frame constituting the lens barrel, on the other hand, then the gap between the fourth lens engaged with the rotary frame and the first to third lens groups engaged with the first lens group frame may change although the optical axis and posture among the first to third lens groups are not influenced thereby. Also, a cam mechanism for moving the four lens groups is necessary for changing the power. Therefore, the mechanism for moving the lens groups becomes complicated, thereby making the lens barrel larger. Further, if dust, dirt, or the like attaches to a sliding portion for advancing and retracting a part of the taking optical system upon a focusing operation of the taking optical system and a moving mechanism, there is a fear that delicate driving for focusing may fail, thereby obstructing focus adjustment.